Z向增强泡沫夹芯阻燃复合材料力学性能

研制了一种Z向玻璃纤维增强酚醛泡沫的高阻燃性复合材料, 并试验分析了承力柱高度、 分布密度、 排布方式及缝编纱细度、 缝合面板层数等结构参数对复合材料力学性能的影响。结果表明: 与普通泡沫夹芯复合材料相比, Z向增强泡沫夹芯复合材料的力学性能得到了大幅度提升; 在承力柱分布密度相同的条件下, Z向增强泡沫夹芯复合材料的力学性能基本不随承力柱排布方式而变化; 承力柱高度、 分布密度及缝编纱细度、 缝合面板层数等结构参数对Z向增强泡沫夹芯复合材料的力学性能有重要影响。     

Thermal Behavior of Nano-TiO2 in Fire-Resistant Coating

The dispersion state of nano-TiO2 particles was studied by using transmission electron microscopy （TEM）and Fourier transform infrared spectroscopy （FT-IR）. Nanoparticles can be fully dispersed by specific hyperdispersant. The improvement of nano-TiO2 in thermal behavior and flame retardation of acrylic polymer and fire-resistant coating was investigated by differential thermal analysis （DTA）, thermogravimetry （TG）and fire-resistant time test. It is demonstrated that nano-TiO2 is helpful for enhancing the thermal stability,anti-oxidation and fire-resistant properties of acrylic polymer and fire-resistant coating.     

新型耐火耐候钢材高温力学性能与本构模型研究

火灾下钢构件断裂破坏是导致整体结构连续性倒塌的主要原因之一,掌握钢材高温断裂性能是研究钢结构抗火承载性能和评估高温后结构安全性的基础。以Q355钢为研究对象,设计光滑圆棒和缺口圆棒试件,进行火灾全过程(升温段、降温段、高温后)拉伸断裂试验,研究复杂应力状态(应力三轴度)和温升历程(峰值温度和拉伸温度)对钢材工程和真实应力-应变曲线、断裂应变的影响,并通过电镜扫描研究其微观断裂机理,结合数值模拟对高温断裂模型进行参数标定。研究表明：火灾全过程下Q355钢材呈现韧性断裂特征,拉伸温度和应力三轴度对其断裂性能影响较大;拉伸温度和峰值温度越高,断裂应变越大,延性越好,高温后断裂性能与常温相似;应力三轴度影响材料断裂性能对温度的敏感性,温升历程影响真实应力-应变曲线塑性段斜率;SMCS断裂模型适用于预测Q355钢材火灾全过程断裂行为,需采用不同参数表征钢材升温段和降温段断裂性能。

     

Mechanical behavior of unstable emulsions

Results of experimental studies of the rheologic properties of unstable macroemulsions of the water-oil type are presented. A region of non-Newtonian behavior of the test emulsions is identified.Translated from InzhenernoFizicheskii Zhurnal, Vol. 30, No. 3, pp. 467–472, March, 1976.     

Mechanical behavior of cracked solids

A general relation between the apparent fracture toughness and the crack growth distance developed earlier is used to study mechanical behavior of a micro-cracked solid in this paper. A one-dimensional model is constructed in which the micro-crack length is regarded as an internal variable. Following the argument in traditional damage mechanics, an incremental form of the constitutive relationship between stress and strain is derived. Numerical results of the theory are used to illustrate the influence of the material parameters appearing in the model.     

Tooth—A natural biocomposite

The inorganic content of human tooth is predominantly hydroxyapatite. The content varies in enamel and dentin. A reversible thermal transformation at 157 C is observed and has correspondence in the dielectric measurements. The dental decay is related to the piezoelectric property of tooth, which is similar to a polar glassceramic. The toughness of tooth is higher than hotpressed hydroxyapatite and owes it to the microstructure signifying the importance of a weak, pliable interface. The hardness is graded, higher for enamel in the crown and very much lower for dentin, to suit their function and environment. The relevance of biomimics in designing materials for advanced performance is discussed.     

Fire resistance of inorganic sawdust biocomposite

The objective of this study was to manufacture fire-resistant biocomposite sandwich plates using waste sawdust as filler and an inorganic potassium aluminosilicate binder. Using binder contents of 29% and 34%, twelve biocomposite plates were fabricated without using any specialized equipment, heat, or pressure, thus producing an environmentally conscious biocomposite material. Several of the plates were strengthened with carbon and glass fiber reinforcements to create a more durable sandwich structure. The influence of binder content and reinforcement type on the heat release rate and smoke emission characteristics were investigated using the OSU heat calorimeter and the NBS smoke chamber, respectively. All specimens passed the Federal Aviation Administration requirements for heat release and smoke emission, the criteria used for evaluation of the test results in this study. Relative to 15 other wood plastic composites that utilize organic polymers, the inorganic biocomposite showed superior heat release rates during 5 min of fire exposure.     

Mechanical behavior of cellulignin based composites

A powder derivative of acid pre-hydrolysis processing of cellulosic wastes, known as cellulignin, was used as filler in resin matrix composites. The flexural mechanical properties of cellulignin-polyester, epoxy or urea-formaldehyde matrix composites was evaluated. The results obtained show that the urea-formaldehyde and epoxy based composites can be used as alternative materials for low cost and low strength applications. Their advantages over the common wooden agglomerates or composites are presented and are based on the fact that cellulignin can be obtained virtually from any cellulosic waste.     

Mechanical behavior of mycelium-based particulate composites

This work investigates the mechanical behavior of mycelium composites reinforced with biodegradable agro-waste particles. In the composite, the mycelium acts as a supportive matrix which binds reinforcing particles within its filamentous network structure. The compressive behavior of mycelium composites is investigated using an integrated experimental and computational approach. The experimental results indicate that the composite mimics the soft elastic response of pure mycelium at small strains and demonstrates marked stiffening at larger strains due to the densification of stiff particles. The composite also exhibits the characteristic stress softening effect and hysteresis under cyclic compression previously observed for pure mycelium. To gain further insight into the composite behavior, a three-dimensional finite element model based on numerical homogenization technique is presented. Model validation is performed by direct comparison with experiments, and a parametric study of the effect of mycelium density and particle size is discussed.     

Preliminary investigation of bioactivity of nano biocomposite

Bioactive biomaterials can form a bone-like apatite layer on their surfaces in the body, which is critical to establishing bone bonding between bioactive materials and living tissue. At present study, the bone-like apatite formation in vitro and vivo on the surface of the nano apatite/polyamide composite was studied, and the bioactive composites implanted into the femora of rabbits were also investigated. The results revealed that the bone-like apatite containing carbonate can form on the surface of the biocomposite both in SBF and dorsal muscle of rabbits, and the composite would form directly combination with the natural bone without fibrous capsule tissue between implant and host bone tissue. All of these indicated that the nano biocomposites have excellent bioactivity and can be used for bone replacement.     

聚氨酯阻燃材料及其应用

介绍了聚氨酯材料的阻燃方法及低烟雾聚氨酯弹性体、阻燃剂微胶囊化等新的研究动 向,并概述了聚氨酯阻燃材料在建筑、运输、灌封胶、涂料等领域的应用。     

Mechanical behavior of axially magnetized permanent-magnet gears

We studied permanent-magnet (PM) gears with axially magnetized permanent magnets and a plane air gap in terms of mechanical behavior. We determined the torque and forces exerted between the two rotors of these devices, using a seminumerical method based on the calculation of the forces between the magnets of the rotors. The study deals with the general behavior of such devices and presents some very interesting configurations for their mechanical stability     

Mechanical behavior of glass polymer multilayer composites

To identify the best reinforcement condition for development of tough glass polymer multi-layer composites (GPMLC) with high failure strain, two such model composite structures were developed. Soda–lime–silica glasses of two different thicknesses viz (A—1.01 mm and B—1.17 mm) were used as the matrix layers. The A-glass and B-glass based GPMLC samples were prepared by a novel, low pressure lamination technique applied to the alternating planar structure of the matrix and reinforcing phases. These GPMLC materials were fabricated with and without a thin sprayed layer of kerosene, between the glass layer and the reinforcing layer in the interface where; the interface was either epoxy (a thermosetting resin) or polyvinyl butyral (PVB, a thermoplastic resin). The GPMLC samples which exhibited stepped load—displacement behaviour in the most pronounced fashion, had the thermoplastic resin at the interface. Most of these GPMLC samples had a thin layer of kerosene intentionally introduced between the glass layer and the reinforcing polymer layer such that a weak interface is obtained. Fractographic evidence suggested that more of controlled delaminaton cracking occurs in such samples. Apart from the chemical nature of the reinforcing polymer phase, the interfacial layer thickness (h _i ) and the interfacial shear stress ( _xy ) were found out to have significant influence on the specific failure load and the failure stress of the current glass polymer multi-layer composites.     

Mechanical behavior of A265 single fibers

The mechanical behavior of A265 high-performance fibers was experimentally investigated at both low and high strain rates. Axial, transverse, and torsional experiments were performed to measure the five material constants on a single fiber assumed as a linear, transversely isotropic material. In order to determine the tensile response of the fiber at high rates, a modified Kolsky tensile bar, also known as a split Hopkinson tension bar (SHTB) for single-fiber tests, was used. The diameter of each fiber was measured individually using a high-resolution scanning electron microscope for accurate stress calculation. A pulse shaper technique was adopted to generate a smooth and constant-amplitude incident pulse to produce deformation in the fiber specimen at a nearly constant strain rate. The tensile strength of the fiber exhibits both rate and gage-length effects.     

Mechanical behavior of Zr-based bulk metallic glasses

Bulk metallic glasses have a very high corrosion resistance and mechanical strength. Bulk metallic glasses show elastic-perfectly plastic behavior with an extended region of elastic strain (≈ 2%). But at room temperature their macroscopic plasticity is weak even though a local plastic strain is observed in shear bands. A relaxation analysis allowed studying micro-mechanisms of plastic deformation and estimating the apparent activation volume (≈ 2000 ų). __________ Translated from Problemy Prochnosti, No. 1, pp. 167–170, January–February, 2008.     

Mechanical behavior of segmented oxide protective coatings

Mechanically and thermally induced fractures were examined in sputtered coatings consisting of an NiCrAlY underlayer, either a thin or a thick transition layer grading from NiCrAlY to ZrO₂, and an outer ZrO₂ layer. A pronounced columnar (fibrous) microstructure was obtained, although the columnar boundaries in the ZrO₂ layers and in the thick transition layers were much more open than in the NiCrAlY, effectively producing a more segmented structure. Some coatings also included a continuous fine-grained outer NiCrAlY sealing or close-out layer.For this complex metal and ceramic coating, a stress applied parallel to the layer plane always resulted in fracture perpendicular to the layer plane along open columnar boundaries. If the transition layer was thick, no fractures other than those at columnar boundaries were observed. If the transition layer was thin, fracture parallel to the layer plane occured in the ZrO₂-rich portion of this layer. When stress was perpendicular to the layer plane, fracture parallel to the layer plane occurred first at the outer ZrO₂(NiCrAlY) interface if an outer NiCrAlY sealing layer was present. Otherwise the ZrO₂-rich portion of the transition layer failed first, followed by fracture in the ZrO₂ layer.     

羟基磷灰石-二氧化锆生物复合材料的制备及其生物相容性

对适用于人体承重部位的人工种植体羟基磷灰石2二氧化锆生物复合材料的制备工艺、微观结构及生物相容性进行了初步研究。用扫描电镜(SEM) 、X 射线衍射(XRD) 和透射电镜( TEM) 对粉体和复合材料进行分析。用体外检测复合材料浸提液对健康青年人末梢血单个核细胞( PBMC) 的激活来评价其免疫相容性。结果表明:1600 ℃无压烧结3h 后的复合材料表面层主晶相为β-Ca₃ ( PO₄ )₂ (β-TCP) 、α-Ca₃ ( PO₄ )₂ (α-TCP) 和CaZrO₃ 相。单纯复合材料和梯度复合材料的表面粗糙度分别为3. 12μm 和1. 95μm。其弯曲强度分别为732. 85 MPa 和689.04 MPa 。HA/ ZrO₂ 复合材料具有免疫相容性, 梯度复合材料的免疫相容性优于单纯复合材料。